This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa76119 from my application entitled MICROWAVE OVEN AND CONTROL METHOD THEREOF filed with the Korean Industrial Property Office on Dec. 6, 2000 and there duly assigned Serial No. 2000-73920.
1. Field of the Invention
The present invention relates to a microwave oven and a method of controlling the same, and more particularly, to a microwave oven and a method of controlling the same, wherein a control signal generator part is controlled based on an oscillation time of a magnetron.
2. Description of the Related Art
Generally, a microwave oven is operated in the following manner. An alternating current (AC) power supplied from a power supply part is applied to a primary coil of an iron-core high voltage transformer so as to generate a high voltage at a secondary coil. The high voltage generated at the secondary coil of the high voltage transformer serves to heat a cathode filament provided in a magnetron and a very high frequency (VHF) energy is emitted from the magnetron oscillated by the applied high voltage. The VHF energy is transformed into heat energy when it encounters water or moisture or an object having water (e. g., food ingredients, etc.) within a closed space, thereby being able to perform a cooking operation.
FIG. 5 is a schematic control block diagram according to a conventional microwave oven. As shown therein, the conventional microwave oven includes a power supply part 101 supplying an AC power, a magnetron 109 generating electromagnetic waves by a high voltage generated from a high voltage transformer 107, a rectifier and smoother part 103 rectifing and smoothing the AC power, an inverter part 105 converting a direct current (DC) power from the rectifier and smoother part 103 into an AC power having a high frequency, a high voltage transformer 107 generating a high voltage by the AC power supplied through the power supply part 101, the rectifier and smoother part 103 and the inverter part 105 sequentially, a control signal generator part 127 generating a control signal, and a controller part 115 positioned between the inverter part 105 and the signal generator part 127.
The controller part 115 includes a D/A (digital/analog) converter part 125 for converting the control signal generated from the control signal generator part 127 and detected from the resonance detector part 121 into an analog signal and applying the converted control signal to an output control or controller part 119, the output controller part 119 controlling to output a frequency of the control signal detected by the resonance detector part 121, and an oscillator part 117 for changing a cycle of the control signal according to the frequency of the control signal outputted from the output controller part 119 and inputs the changed cycle into the inverter part 105. The controller part 115 further includes an on-off starter part 123 for controlling an on-off operation of the oscillator part 117 according to the control signal generated from the signal generator part 127 and controlling a soft start of the oscillator part 117.
Hereinafter, the related art will be described with reference to FIG. 6 which is a graph showing waveforms of a control signal from a conventional microwave oven. Referring to this figure, a control signal is applied to the magnetron 109, the control signal having the same width of pulse in a cold state, when the magnetron is driven at first after the oven is manufactured or the magnetron has not been operated for a predetermined period of time, and in a hot state, when a filament of the magnetron 109 is heated to a predetermined degree of temperature over the predetermined temperature.
Where the same control signal is applied in the hot state, a relatively large amount of electric current is applied, when the filament of the magnetron is heated over the predetermined temperature, thereby generating a condition of surge temporarily. In other words, over-current and/or over-voltage are generated, which causes a stability of the circuit to be lowered. Also, this causes the magnetron to be overloaded, generating a condition of noise temporarily.
Accordingly, the present invention has been made keeping in mind the above-described shortcomings, and an object of the present invention is to provide a microwave oven and a method for controlling the same, wherein surge and/or noise can be controlled on the basis of the time of oscillation of the magnetron.
This and other objects of the present invention may be accomplished by the provisions of a method for controlling a microwave oven including a power supply part supplying an AC power, a high voltage transformer generating a high voltage with the AC power generated from the power supply part, a magnetron generating electromagnetic waves with the high voltage generated from the high voltage transformer, and a control signal generator part supplying a control signal to the magnetron, including the steps of: setting up a reference oscillation time; measuring the time when the magnetron starts being oscillated according to the control signal; comparing the reference oscillation time with the oscillation start time; and adjusting a pulse width of the control signal where the reference oscillation time is longer than the oscillation start time.
Preferably, the step of setting up the reference oscillation time includes the substeps of: setting up an arbitrary oscillation time as a set-up oscillation time; measuring the oscillation start time of the magnetron; comparing the set-up oscillation time with the oscillation start time; and adjusting the set-up oscillation time so as to be equal to the oscillation start time where the set-up oscillation time is longer or shorter than the oscillation start time, and setting the adjusted set-up oscillation time as the reference oscillation time.
Effectively, the method further includes the step of: setting the set-up oscillation time as the reference oscillation time if the set-up oscillation time is equal to the oscillation start time.
According to another aspect of the present invention, the above and other objects may also be accomplished by the provision of the microwave oven including a power supply part supplying an AC power, a high voltage transformer generating a high voltage with the AC power generated from the power supply part, and a magnetron generating electromagnetic waves with the high voltage generated from the high voltage transformer, including: a control signal generator part generating a control signal with a predetermined pulse width; a counter counting the time when the magnetron starts being oscillated according to the control signal; and a controller part adjusting the pulse width of the control signal where the oscillation start time counted by the counter is shorter than a predetermined reference oscillation time.
Preferably,the controller part compares the set-up oscillation time with the oscillation start time of the magnetron, adjusts the set-up oscillation time so as to be equal to the oscillation start time where the set-up oscillation time is longer or shorter than the oscillation start time, and setting the adjusted set-up oscillation time as the reference oscillation time.
Effectively, the controller part sets the set-up oscillation time as the reference oscillation time where the set-up oscillation time is equal to the oscillation start time.